Fire salamanders glow green and cyan under ultraviolet light, scientists find

Scientists have discovered that fire salamanders (Salamandra salamandra) glow under ultraviolet light, a finding that came as a surprise in a species whose skin chemistry has been studied for decades.

The phenomenon occurs when compounds in the salamander's skin absorb ultraviolet light, which humans cannot see, and reemit that energy as visible light, producing the green and cyan colors. Known as biofluorescence, it requires an outside source of illumination and should not be confused with bioluminescence: animals such as fireflies produce their own light through chemical reactions, while fluorescent organisms must first absorb light from their surroundings.

Scientists once believed biofluorescence occurred almost exclusively in marine organisms, with scorpions standing out as an unusual land example. More recent studies have challenged that assumption, identifying fluorescent properties in a growing variety of terrestrial animals, including reptiles, birds and amphibians.

Bernat Burriel, a researcher at the Museum of Natural Sciences in Barcelona and the study's first author, said: "It is fascinating that such a well-studied species still harbors unknown phenomena like this. It reminds us that even the most familiar organisms can hide secrets that are only revealed when they are observed with new tools."

The biological purpose of the glow remains uncertain. One possibility is that it helps salamanders recognize one another or assess potential mates. Another is that it makes their warning coloration more noticeable to predators. Martin Kaltenpoth, director of the Department of Insect Symbiosis at the Max Planck Institute for Chemical Ecology and a co-author of the study, said: "Fluorescence meets several criteria that suggest a communicative function. It could help salamanders detect each other in nocturnal or particularly dense environments, or act as an additional defense signal."

Researchers note that full moonlight contains a greater proportion of ultraviolet and violet wavelengths than daylight. Under moonlit conditions, fluorescence could create small green and cyan highlights against the salamanders' yellow markings, potentially making them easier for other salamanders to spot.

The chemical responsible for the glow has not been identified. Andrés Brunetti, a researcher at the Max Planck Institute for Chemical Ecology and a co-first author, said the presence of the fluorescent compound was surprising because salamander skin secretions had been studied chemically for decades with no published reports on fluorescence. Salvador Carranza, a researcher at the IBE (CSIC-UPF) and another co-author, said everything indicates it is a molecule unknown until now in this species, and identifying it will be key to understanding its origin and function.

The discovery comes as the International Union for Conservation of Nature classifies fire salamanders as "vulnerable" on its Red List of Threatened Species. The species typically inhabits damp forests, streams and mountainous regions, where habitat destruction and fragmentation increasingly threaten its survival. Understanding whether fluorescence influences communication, mating or predator avoidance could contribute to conservation efforts.

The research also involved scientists from the Institute of Subtropical Biology and the Catalan Society of Herpetology, and forms part of a pioneering amphibian conservation project in Catalonia supported by the Barcelona Zoo Foundation.